Two-Channel Bioprotonic Photodetector.

Merging biological systems with electronic components requires converting biological ionic currents into electrical signals. Previously, we coupled green-light-activated transport of protons by a palladium-binding version of H. turkmenica deltarhodopsin (HtdR) with electronic signal generation by exploiting palladium hydride (PdHx) formation on palladium (Pd) electrodes. Here, we broaden the scope of these devices by showing that blue proteorhodopsin (BPR) from marine bacteria is a suitable proton pump for expanding their spectral range. After engineering BPR for Pd binding and high-level expression in E. coli and after demonstrating that the fused Pd-binding domain is properly oriented to bring exiting protons to the surface of Pd/PdHx contacts, we take advantage of the pH tunability of the BPR absorption spectrum to construct HtdR- and BPR-based devices with light absorption maxima, and thus photocurrent maxima, separated by 37 nm. These devices exhibit wavelength-dependent photocurrent production when illuminated between 450 and 600 nm, opening the door to the development of biological cameras.